Normal
From Halopedia, the Halo wiki
Hordes of aliens vie to destroy you, but nerves of steel and a quick trigger finger give you a solid chance to prevail.
Summary
Normal is the default difficulty rating; it's not too hard, but not too easy. The enemies will not cower as much, and few Grunts will throw Plasma Grenades. It is ranked 2nd in the list of 4 difficulties. In addition this difficulty is another good starting level for beginners to the Halo series as is Easy Mode.
Normal is a little harder than easy but players can move through levels relatively easily. This difficulty doesn’t ruin your gaming experience by being too hard and is hard enough to impede progress.